1. Technical Field
The present invention relates to an engine having first and second intake ports for each cylinder (or combustion chamber), and more particularly to improvements to intake ports of such an engine.
2. Background Art
If a plurality of intake ports is formed for a single cylinder (or combustion chamber), the total effective area for air intaking is enlarged and various advantages arise. Most typical engines having a plurality of intake ports are three-valve engines (two intake ports and one exhaust port) and four-valve engines (two intake ports and two exhaust ports).
One example of the four-valve engine is disclosed in Japanese Patent Application, Publication No. 50-135421. FIG. 21 of the accompanying drawings is one figure of this publication. As shown, two intake ports 1 and 2 extend parallel to each other and perpendicular to a direction of a crankshaft (not shown). The first intake port 1 is provided for inertia supercharging and the second intake port is provided for normal air intake. The intake air entering the composition chamber 4 from the first intake port 1 and that from the second intake port 2 are different in speed and pressure. Thus, when these two intake airs enter a single combustion chamber 4, they intervene with each other in the combustion chamber 4 and a turbulence occurs. Because of the turbulence, the intake air mixes with a fuel in a desired manner. As a result, a combustion of less HC, CO and smokes is realized. Numeral 3 designates an intake valve and 5 designates an exhaust valve.
An example of three-valve engine is seen in Japanese Utility Model Application, Publication No. 59-192625. A fundamental teaching of this publication is illustrated in FIG. 22 of the accompanying drawings. As shown, two intake ports 10 and 20 extend parallel to each other and perpendicular to a crankshaft direction (not shown)to generate first and second swirls "alpha" and "beta", respectively. Means M is provided for deviating the flow direction of the second swirl "beta" generated in the second intake port 20. The second swirl "beta" is deviated such that the second swirl "beta" from the second intake port 20 and the first swirl "alpha" from the first intake port 10 flow in the same direction in a combustion chamber 50. The swirl deviation means M is a stationary shroud in FIG. 22, but it is a masking plate in another embodiment. Incidentally, numeral 30 designates an exhaust port, 40 designates a spark plug and 01 designates a center off the combustion chamber 50. If the swirl deviation means M is not provided, the first and second swirls rotate in opposite directions in the combustion chamber 50. In other words, these swirls intervene with each other in the combustion chamber 50 and hey are weakened by the opposite swirls. If the swirl is weak in the combustion chamber. a large amount off smoke results in the case of diesel engines.
The above-described conventional arrangements have the following problems:
(i) The layout of intake ports in the arrangement of Japanese Patent Application, Publication No. 50-135421 is complicated and the cylinder head must be designed with larger dimensions; and PA1 (ii) The air flow direction adjusting means in Japanese Utility Model Application, Publication No. 59-192625 employs a masking plate or a stationary shroud which becomes an obstacle to the second swirl and raises throttling loss. Therefore, the intake efficiency raised by a plurality of intake ports is counterbalanced.